1. Field
The present disclosure relates generally to aircraft and, in particular, to forming stringers in an aircraft. Still more particularly, the present disclosure relates to a method and apparatus for compacting layers of uncured composite material for a composite stringer.
2. Background
Aircraft are being designed and manufactured with ever increasing percentages of composite materials. Composite materials are used in aircraft to decrease the weight of the aircraft. This decreased weight improves performance features such as payload capacity and fuel efficiency. Further, composite materials provide longer service life for various components in an aircraft.
Composite materials may be tough, light-weight materials created by combining two or more functional components. For example, a composite material may include reinforcing fibers bound in a polymer resin matrix. The fibers may be unidirectional or may take the form of a woven cloth or fabric. The fibers and resins may be arranged and cured to form a composite structure.
Using composite materials to create aerospace composite structures may allow for portions of an aircraft to be manufactured in larger pieces or sections. For example, a fuselage of an aircraft may be created in cylindrical sections to form the fuselage of the aircraft. Other examples include, without limitation, wing sections joined together to form a wing or stabilizer sections joined together to form a stabilizer.
In manufacturing composite structures, layers of uncured composite material may be laid up on a tool. The layers of uncured composite material may be comprised of fibers in sheets. These sheets may take the form of, for example, without limitation, fabrics, tape, tows, or other suitable configurations for the sheets. In some cases, resin may be infused or pre-impregnated into the sheets. These types of sheets are commonly referred to as prepreg.
The different layers of prepreg may be laid up in different orientations and different numbers of layers of uncured composite material may be used depending on the desired thickness of the composite structure being manufactured. These layers of uncured composite material may be laid up by hand or by using automated lamination equipment such as a tape laminating machine or a fiber placement system.
Laying up layers of uncured composite material to form different structures in an aircraft may be a complex and time-consuming task. For example, a section of a fuselage includes laying up layers of uncured composite material for the walls of the fuselage.
Additionally, other features may be laid up or placed onto these layers for curing at the same time. For example, stringers on the interior walls of the fuselage may be laid up along with the walls for the fuselage itself. For example, layers of uncured composite material in the form of a stringer may be laid up on a tool. This tool may be an inner-mold line (IML) tool when the stringer is laid up with other structures to form a composite structure. In other illustrative examples, the tool may be used only for compacting the stringers. These layers may be compacted after being placed on the tool. A compacting device is used to hold the shape of the stringer and compact the stringers before curing the stringers with the other layers of uncured composite material for the wall of the fuselage.
These compacting devices may take various forms. For example, a bladder, a mandrel, or some other suitable device may be placed against the inner wall of the stringer. After the stringers have been placed on the IML tool, a vacuum bag may be placed over the stringers. A vacuum may then be applied to the vacuum bag to compact the layers of uncured composite material for the stringers. When a vacuum is applied, air and other gases in the vacuum bag are drawn out of the vacuum bag.
The stringers are often compacted in batches. In other words, stringers awaiting other stringers to be placed on the IML tool are not compacted until the additional stringers in another batch are ready. The stringers awaiting processing may change from the desired shape or shift forms before compactions occur for the batch of stringers.
Additionally, the process of installing the vacuum bag and applying the vacuum is a labor-intensive job performed by operators. The vacuum bag is placed over the stringers. The edges of the vacuum bag are sealed. Thereafter, a vacuum is drawn in the vacuum bag such that pressure is applied on the compacting devices in the stringers.
The vacuum may be drawn for various periods of time. For example, the compaction may require about thirty minutes. During this time, the operators and other processes in forming the fuselage section are put on hold. After the stringers have been compacted, the vacuum bag is removed and the compaction devices are also removed from the stringers. Thereafter, any additional layers of uncured composite material may be laid up on the tool for curing. Thereafter, the fuselage section and the stringers may be cured to form the fuselage section.
This process is complex and time-consuming. The complexity and time needed to perform these operations may result in taking more time than desired to form a composite fuselage section for an aircraft. Therefore, it would be desirable to have a method and apparatus that takes into account at least some of the issues discussed above, as well as other possible issues.